US patent publication no. 2009/0236777 A1 discloses a method for making a crank of a bicycle includes preparing a prepreg material and a bladder, heat-pressing the prepreg material and bladder, cutting the prepreg material and the bladder to form two engaging sections to engage with two connectors, wrapping a carbon-fiber cloth, and heating the prepreg material and first and second connectors that is wrapped by the carbon-fiber cloth.
However, the conventional bicycle crank may have an insufficient strength. To provide a crank with a larger strength, the crank may be made by winding multiple layers of composite material (prepreg) around a core, followed by curing. In this case, the weight of the bicycle crank would be undesirably increased.
US patent publication nos. 2007/0186719 and 2008/0272572, and European patent publication no. 2921291 A1 also disclose bicycle crank arms.